Currently, 2G/3G (2nd Generation/3rd Generation, 2nd generation mobile telecommunications technology/3rd generation mobile telecommunications technology) networks have been widely deployed in many regions. With rapid development of communications technologies, next-generation evolved networks, such as an LTE (Long Term Evolution) network, have covered some urban areas and telephone traffic hotspot regions. Therefore, an evolved network and a 2G/3G network coexist in these areas. In order to reduce costs, a Single RAN (Single Radio Access Network, single radio access network) solution for sharing a radio access network device is generated. A Fusion Network (fusion network) provides a technology evolution method for the Single RAN, where a cross-system interoperability technology is a key technology for implementing fusion of networks of the Fusion Network in the Single RAN solution.
During an existing cross-system interoperability process, an air interface and a terrestrial interface are in one-to-one correspondence, and an NAS (Non Access Stratum, non-access stratum) interface and the air interface/terrestrial interface are also in one-to-one correspondence, which is related to network standards of the NAS interface, the air interface and the terrestrial interface. For example, a UMTS (universal mobile telecommunications system) network UE (user equipment) is connected to a UMTS core network by using an air interface and a terrestrial interface of a UMTS network. If the UE connected to the UMTS network needs handover to an LTE network, the following operations need to be performed: a UMTS access network sends a handover request to a UMTS core network; the UMTS core network sends the request to a target LTE core network; the target LTE core network sends the handover request to a target LTE access network; the target LTE access network performs air interface resource configuration and returns a handover response to the LTE core network; the LTE core network then sends a handover command message to the UMTS network UE by using the terrestrial interface and the air interface of the UMTS network; and the UMTS network UE configures an air interface connection according to a received air interface resource configuration requirement, and then accesses the target LTE network. Such a inter-standard interoperation has a complex process, much signaling, and a long delay, which severely compromises user experience.